From U.S. Pat. No. 3,882,965 to Loomis et al. it is known to employ a simple ladder adapted to be installed on a truck bed wherein a lower fixed step portion and an upper top and side rail unit are integral therewith, and wherein a swing step is pivotally mounted to internal channel reinforcements for securing the ladder to the truck bed.
U.S. Pat. No. 4,079,815 to Cormier describes an extensible step assembly having steps secured to section of extensible or telescoping arms whereby the assembly can be moved from a retracted compact position to an extended position for use. It is taught that the extensible arms are pivotally secured to a frame which can be bolted directly to a truck or other platform, and there is no provision for personnel support railings or handles extensible above the pivotal attachment to the frame.
Other ladders for vehicles which are similarly permanently mounted thereto, or which require modification of the vehicle, are described in U.S. Pat. No. 4,333,547 to Johansson; U.S. Pat. No. 4,191,388 to Barksdale; U.S. Pat. No. 3,826,337 to Liptak et al.; and U.S. Pat. No. 3,033,309 to Fugere. Moreover, none of the vehicular ladders provide for retractable personnel supports or handles substantially above the top of the runged portion of the ladder assembly.
Other references pertinent to ladder assemblies and constructions include U.S. Pat. No. 3,005,513 to Larson; U.S. Pat. No. 3,093,216 to Dunham; and U.S. Pat. No. 4,261,436 to Stillman, Jr.; and French Patent 1,351,740 to Frassetto.
There is, however, an as yet unfilled need for a portable ladder assembly which is adapted to be removably mounted to a truck trailer. The ladder would be desirably positioned or stored below the top surface of the truck bed when not in use to remain out of the way during transportation of a load on the truck bed, or during loading and unloading. However, the ladder would desirably have support handles extensible above the runged portion of the ladder to facilitate climbing by personnel. In addition, the ladder would desirably be storable or positionable sufficiently above the surface of the road or other grade-level surface so it is not subject to exposure to damaging elements during transportation of the truck trailer to which the ladder assembly is attached. However, the ladder would desirably have a bottom portion adjacent grade level during climbing by personnel to avoid excessive bottom-rung heights. Furthermore, the ladder must be adapted for readily removing the ladder from one truck trailer and quickly installing it on another, ideally without welding, cutting, drilling or similar procedures requiring power tools and/or modification of the truck trailer bed. As far as Applicant is aware, there is no prior art teaching or suggesting such a ladder assembly.